This invention relates generally to a voltage regulator having an output which drives a liquid crystal display and more particularly to a voltage regulator having an output which compensates for the temperature characteristics of the threshold and saturation voltages of the liquid crystal display elements. An impressed effective voltage which makes a ten percent contrast in the liquid crystal display is considered to be the threshold voltage and an impressed effective voltage which makes a ninety percent contrast on the liquid crystal display is considered as the saturation voltage. At colder temperatures higher effective voltages must be impressed to produce the same contrast. The threshold and saturation voltages have negative temperature coefficients and plot as substantially straight lines. When a liquid crystal is operated by a multiplex time sharing driving method, the impressed effective voltage to make the contrast in the liquid crystal display greater than ninety percent changes in accordance with a duty ratio 1/N, where N is a natural number. The impressed voltage to make the contrast of the display less than ten percent is also varied by the same duty cycle ratio 1/N. When a dot matrix display is used, because the value of N is 7 to 16, or even greater, the ratio of voltage which provides the ninety percent contrast relative to the voltage which provides the ten percent contrast falls as the value of N increases. In such matrix display embodiments, at the low temperature end of the operating range, cross talk is produced in the liquid crystal.
What is needed is a voltage regulator for a liquid crystal display having an output which compensates for the temperature characteristics of the liquid crystal elements and operates without cross talk.